Snap switch plunger construction



5Septv.*19,`1944. A A. L RICH; ErxAL A SNAP SWITCH PLUNGER CON-STRUCTIUN Filed June 26', 1942 ,kmlm

Patented Sept. 19, -1944 SNAP SWITCH PLUNGER CONSTRUCTION Arthur L. niche and Ben J. Rush, Freeport, nl.,

asslgnors to Micro Switch Corporation, Freeport, Ill., a corporation of Illinois Application June 26, 1942, Serial No. 448,598

(Cl. 20o- 67) 9 Claims.

This invention relates to electric snap switches of the small, compact, precision type shown in McGall Patent 1,960,020, issued May 22, 1934,

and is more particularly concerned with an improved operating plunger construction. In referring to the switch of our invention as a precision switch, it must be understood that we mean one which operates in response to very slight movement of the operating plunger and one which is intended to operate conslste'ntlyiat the same position of its plunger. One commercial construction of the switch, for example, has the switch mechanism in amolded housing of insulating material, occupying less than one and one-half (1%) cubic inches of space, and operating in response to a plunger movement of the order of one ten .thousandth (0.0001) inch between on" and "oiif with only a few ounces of operating force, although controlling directly loads of the order of a thousand watts on alternating current.

Because the switch is a precision device, and because it 4operates in response to such slight motion and pressure, extreme care and accuracy are required in manufacture, and the'operation of the switch can be impaired very materially by slight changes or misadiustments of its mechanism. Even slight misadjustments or mislocations of its parts will-cause the switch to exhibit operating characteristics far inferior to those of a properly constructed switch. The switch must be manufactured to close tolerances and protected against any injury which might result in a disarrangement of its operating mechanism.

` While the McGall switch operates satisfactorlly for many purposes and has certain desirable characteristics, it has other characteristics which leave it unsuited to other applications and it presents a number of manufacturing diillculties.- For example, switches made in quantity production have exhibited widely. different operating characteristics, .and have even changed their characteristics in use. Consequently, they could .not be made easily interchangeable for replacement purposes, and the switch could not conveniently be fitted into the design of other apparatus, the characteristics of which had to be matched to the characteristics oithe switch.

' These shortcomings have seriously restricted the commercial use and value of the McGall switch, and their correction has required experiment and development looking to structural improvements.

Due to the fact that the switch with which our tioned-a change in the operating characteristics must operate with a high degree of precision, its construction and arrangement of parts presents a number oi'v difllculties'not encountered in'larger switch structures.l 'I'heoperating'plunger, as will be pointedout later, has presented a difficulty of this sort, one which would not have been noticed, let alone appreciated, in a large switch. The small space available inthe coinpact `switchesv with which our invention deals and the fact that the switch is intended to operate with only a fewounces of operating force bending of certain parts to make the switch conform. to a standard so far as operating characteristics are concerned. For example, ithas been Ythe .practice to bend the stationary contacts after assembly of the switch to obtain the desired functioning.

In switches of the precision type mentioned, it has been diflicuit tounaintain the desired aocuracy in operation due to the fact that the" slightest change in the relationship of the operating plunger to the snap action spring while in.

service was sufficient to 'make a very appreciable change in the operating characteristics of the switch, and the switch manufacturer could not, therefore, with any definite assurance recommend a switch as being adaptable for a speciiio m03? requiring certain speciilc operating characteristics. It has been the practice, as illustrated for example in` Riche' Patent 2,181,068, to provide the operating .plunger in the form'of a highly P01- ished stainless steel pin molded into a. head of insulation material for. contact with the snap action spring, thereby insuring freedom from -electrical leakage to the plunger itself. In the" molding operation, the' pin in one plunger was apt to assume a slightly different relationship to the molded head from the pin in another plunger, and the slightest eccentricity of the molded head we found caused the diillculty menoi the switch upon rotation of the It is. therefore. the 'principal object of our in vention tolprovide an operating plunger the molded head of which has a star-shapedskirt portion of such dimensions that thev plunger cannot turn out of-a set position within the nous` although it issubstantially free to move frictional resistance to movement is reduced tol a minimum, the relieved sidesof the head furthermore aiording extra space within the housing for other operating elements.

The invention will be better understood asA reference is made in the following description to the accompanying drawing, in which-v Fig-ure 1 is atop view of a switch made in accordance with our invention, this view showing the actual size;

Fig. 2 is a longitudinal section on an enlarged scale taken on the line 2-2 of Fig. 1;

Fig. .3 is a top view with the cover removed so as to show theplunger and `its relationship in the housing to the snap action spring; Fig. 4 is a cross-section on the line 4-4 of Fig. 2 to further illustrate the relationship of the operating4 plunger to the other parts of the switch, and

Fig. 5A is a more orV less diagrammatic view, partly in section and partly in side elevation, to

l illustrate by exaggeration in the eccentricity of the head of the plungerwith respect to the pin the inaccuracy that is apt to be introduced and the resultant change in the operating characteristics of the switch, where they plunger is not safeguarded againstrrotation.

The same reference numerals are applied to corresponding parts throughout the views.

'I'he switch comprises a housing 6 of insulation material consisting of a base 1 and a cover 8 for enclosing the switch mechanism. 9 is a metal insert in the base carrying a screw I0, and II is an anchor held by the screw. The insert 9 provides an electrical connection between the anchor II and an external terminal screw I2. The anchor I I supports a pair of compression spring members I3 and a tension spring member I4 of the A snap mechanism of theswitch. The two side compression members I2 and the central tension member I4 ot the snapmechanism are stamped integrally from a single sheet of thin spring material, so that the several spring members to. gether constitute a three-pronged piece I5. This piece carries a. movable contact I6 which, when the switch operates. moves with snap action between the stationary contact I1 and the insulating abutment I8 on the base. The contact I1 has a screw I9 mounting the same on another metal insert 20 in the base 1 whichprovides an electrical connection between the contact I1 and an external terminal screw 2i.

The compression.I members I3 areA pivotally supported in notches 22 in the ends of the legs of the U-shaped anchor II. The tension member I4 is Asupported in cantilever fashion under the head of the screw I at the base of the U of the anchor I I and passes near the pivotal axis of the two compression members I 3 in the notches 22. If pressure is applied to the tension member I4 to deect its tension center line across the pivotal axis of the two compression members I3, the spring members I3 and I4 will coact'to snap the movable contact I Ifromits one extreme position to the athen-When the tension member it is forced downytle movable contact I 6 is vsnapped out of engagement with the stationary contact I1,

the snap actl'onmember Il coming into engagement with the abutment I8, but when the pressure is released, the conta'ct 'I6 snaps back to its normal position in engagement with the stationonly to show the general relationship of the parts mentioned.

The operating plunger with which our invention is especially concerned is designated by the l reference numeral 23 and includes a highly polishedstainless steel pin 24 onto which is molded a head 25 of insulation material. The pin 24 is reciprocable in a hole 26 in the cover 8 to depress the head 25 and deflect the tension member I4 downwardly to operate the switch. The pressure is applied to the tension member I4 by a central spherical projection 21 on the bottom of the head at a point between the point of support of the tension member under the head 25 of the screw I0 and the point of support of ,the compression springs I3 in the notches 22. The head 25 overhangs the two legs of the anchor II so that `the anchor serves as a stop to limit the downward movement of the plunger, the 30 movement being limited to a little more than that necessary to deect the tension member I4 to the point at which it moves with snap action to the opposite extreme position. 'I'he head 25 is of generally cylindrical form but has a starshaped skirt portion 28 formed thereon inter mediate' the ends thereof in a plane substantially normal to the axis of the pin 24 of such dimensions that the light sliding contact ot the rounded points 29 with the smooth inner side 40 walls 30 of the housing will prevent rotation of the plunger with no perceptible increase in the resistance to the movement `of the plunger. Bearing in mind the fact that switches of this kind must be operable with only a few ounces of force applied and are supposed to be so accurate in their operation that they can be used reliably for gauging," it can be seen how important it is that any means provided yto prevent rotation of the add perceptibly to the resistance to movement.

The reason it is so important to prevent 'rotation of the operating plunger is illustrated in ,Fig. 5, by showing the head 25 in exaggerated eccentricity with respect to the pin 24 and indieating in full and dotted lines the extent to which rotation of the plunger through one hun'` dred eighty degrees (180) affects the position of the projection 21 measured longitudinally of the tension member I4. Assuming any eccentricity of the head respect to the pin 24, it is clear that the'pro- .jectionv 21 in one extreme position, shown in full lines, will cause the switch to operate with much more movement of the plunger than -in the opposite extreme position, indicated in dotted lines.

Needless to say. the switch also changes with any alteration in the position of the projection 21 lengthwise with respect to the tension memberl I4, the plunger 22 having greatermechanical advantage when the projection 21 is in the full line position than when it is in the opposite extreme position indicated in dotted lines. It is impossible to mold the heads 25 on the pins 24 accurately enoughto insure the same point ot contact of the pro` operating plunger 23 must not 25 of'whatever degree with the force required to operate itially as and for the purpose described.

jection 21 on the tension member Il throughout threehundred sixty degrees (360) rotation of the plungers. Such inaccuracy as is bound to occur is practically reduced to rero by limiting mg by sliding contact of the points or the' skirt at the edge thereof with the walls of the housin. 3. Anarticle of manufacture as set forth in claim 2, wherein the points of the star-shaped thereafter of any change in the operating characteristics of the switch. Relievingsthe sides of the skirt portion 28 between the points 29, as indicated at 3|, has a two-fold advantage, one being that it makes for reduced friction drag by avoiding any likelihood of surface to surfacer contact between the skirt and the walls of the housing, there being only line contact at widely spaced points, and it avoids' any `likelihood of the skirt coming in contact with other operating elements of the switch, the head of the screw 10, for example, being assured of ample clearance with respect to the skirt 2B by virtue of the relief between the points 29 on that sideof the yhead 25, as clearly indicated in Figs. 2 and 3.

It is believed the foregoing description conveys a good understanding of the objects and skirt portion are of thin cross-section, of substantially semi-circular form and are struck on ar of small radius.

, 4. For use in a spring snap mechanism of the class described, comprising a housing, a bowed. thin, elongated snap action leaf spring, and a support therefor in the housing, said housing having e a guide and having side wallspresenting smooth advantages of our invention. The appended claims-have been drawn to cover all legitimate modifications and adaptations.

We claim:

1. As an article of manufacture, an operating plunger for close accuracy operative engagement with the snap action element of an electric snap switch of the character described, and to have close accuracy, non-rotary, reciprocatory operation but with a free fit between the substantially parallel side walls of the housing of said switch,

said plunger comprising a metallic pin for reciprocation of the plunger and a head of non-- metallic insulating material mounted on one end thereof in substantially concentric relation thereto, having a central projection on the side thereof opposite said pin for operative engagement with' the snap action element of the switch, said head having a `generally rectangular, radiallyprojecting skirt portion in a planesubstantially normal to the axis of the pin adapted to'have free but accurate non-rotary slidable guiding engagement on its opposed edge portions with the side walls of the housing, the skirt portion being cut awaybetween the corners thereof, substan- 2. As an article of manufacture, an operating `plunger for close accuracy operative engagement with the snap action element of an electric snap hswitch of the character described, and to have close accuracy, non-rotary, reciprocatory operation but with a free lfit between the substantially parallel side walls of the housing of said switch,

`said plunger comprising a metallic pin for reciprocation of the plunger having mounted on one end thereof a head of non-metallic insulating material of substantially cylindrical form in sub- I stantially concentric relation with the pin having a central projection on the side thereof` opposite 'said pin for operative engagement against the snap action element of the switch for operation thereof upon-longitudinal movement of the pin,

the head havin! rigid-therewith and projecting radially therefrom a star-shaped skirt vportion in a plane substantially normal to the axis of the pin, said skirt portion being ofsuch width dimensions inrelation to the inside width dimensions ofthe housing that'the plunger can reciprocate inner surfaces substantially parallel to one another on opposite sides of said spring, an operating plunger comprising a |pin re'ciprocable in the guide, and a head mounted on the inner end of said pin having a downward projection on the bottom thereof adapted to engage the leaf spring at a point intermediate the ends thereof for deflection of the spring under pressure applied to said pin, said head having lateral projections which by sliding engagement with the aforesaid smooth inner surfaces prevent rotation of the plunger relative to said spring.

5. For use in-a spring snap mechanism ofthe class described, comprising a housing, a bowed, thin, elongated snap action leaf spring, and a support therefor in the housing, said housing having a. guide and having side walls presenting smooth inner surfaces substantially parallel to one another on opposite sides of said spring, an operating plunger comprising a metal pin reciprocable in the guide, and a head of non-metallic insu lating material mounted on the inner end of said pin having a downward projection on the bottom thereof adapted to engage the leaf spring at a point intermediate the ends thereof for deflection 'of the spring under pressure applied to said pin,

said head having a readily projecting star-shaped tion leaf spring, and a support therefor in the housing, an operating plunger comprising al pin reciprocable in the guide provided therefor, and a head mounted on the inner end of said pin having a downward projection on the bottom thereof adapted to engage the leaf spring at a point intermediate the ends thereof for deflection of the spring under pressure applied to said pin, said operating plunger having means acting between the side walls of said housing and the peripheral portion of the head in radially spaced relation to the pin to hold the plunger against turning while permitting free reciprocation thereof.

7. For use in a spring snap mechanism of the class described, comprising a housing having a guide therein, a bowed, thin, elongated snap action leaf spring, .and a support therefor in the l. housing, an operating plunger comprising a pin 'operating plunger having means to hold the plunger against turning while permitting free reciprocation thereof.

8. For use in a spring snap mechanism ofthe freely within the housing while held against turnclass described, comprising a housing having a operating plunger having means limiting within close limits the rotation of said head with respect to said housing while permitting free reciprocation thereof.

9. The combination in a switch of the precision type having a snap action leaf spring and a housing therefor of an operating plunger comprising a metallic pin mounted in the housing for reciprocation therein and a head of insulating material mounted on one end thereof within le jection with the spring.

the housing in substantially concentric relation thereto, said head having a central projection on the side thereof opposite said pin for engagement against said spring to operate the same by pressure thereagainst upon axial movement of the plunger, said` head also having a thin radially projecting skirt portion of generally rectangular. shape in a plane substantially normal to the axis of the pin having a width slightly less than the distance between the side walls of the housing for free but accurate non-rotary, Slidable guiding engagement on its edges against the side walls to prevent rotation of the plunger and consequent change ofthe point of engagement of the pro- ARTHUR L. RIGHE. v BEN .11. RUSH. 

